Typically, thermosetting foam products are prepared by the use of a phenol-formaldehyde resin, a blowing agent and a strong acid catalyst. Such thermosetting foam products are often characterized by having a fairly brittle foam structure, with low compression strength and exhibiting high friability and brittleness properties. Such phenolic foams, usually have an open-cell foam structure and very little, if any, strength at low densities; for example, below about 2.5 pounds per cubic foot. These phenolic foams are difficult to burn, melt or smoke, in that they are characterized substantially by methylene linkages. However, such phenolic foams are not generally commercially acceptable, because of low compression strength, poor insulation value and the corrosive characteristics of the foam.
Modified phenolic foams have been prepared employing polyisocyanates, to produce a phenolic urethane foam product. For example, U.S. Pat. No. 3,948,824, issued Apr. 6, 1976, hereby incorporated by reference, describes a modified urethane benzylic-ether phenolic foam product. The cellular polymeric reaction product is produced by the reaction of a benzylic-ether phenolic foam in the presence of a liquid methylene diisocyanate-type isocyanate, a blowing agent and amine catalysts, to form a benzylic-ether phenolic urethane foam product. The reaction mixture foams and cures spontaneously in an exotherm into a tough, non-friable foam. The resulting foam product is closed-cell and has good insulation properties; however, the foam product, because it burns and smokes in a manner very similar to a urethane foam product made from aromatic polyols, does not have commercially acceptable flame-retardant properties, probably due in part to the presence of urethane linkages in the resulting foam mass.
Another difficulty associated with benzylic-ether phenolic urethane foams is that the resulting material is quite reactive, and, therefore, it is difficult to control the nature and extent of the reaction and is difficult to produce the thermosetting foam in a consistently high-quality manner in standard production foaming equipment, due to the very high reactivity of the ingredients.
It would be desirable to prepare a phenolic foam material which provides for a substantially closed-cell ultra low density foam structure of low friability and which exhibits nonburning and nonsmoking characteristics.